4 PRACTICAL ORGANIC CHEMISTRY by heating the substance strongly with magnesium powder and moistening the cold product with water. Magnesium phosphide is formed and is decomposed by the water, giving phosphine which is readily detected by its smell. Quantitative Estimation. Carbon and Hydrogen.—The principle of the method is that described under qualitative examination^ but the substance and the products of combustion, viz., carbon dioxide and water, are weighed. The following app'aratus is required. 1. An Rrlenmeyer or other form of Combustion Furnace.— The usual length is 80-90'cm. (31-35 in.), and it is provided with 30 to 35 burners. Flat flame burners are undesirable. 2. A Drying Apparatus.—A form of drying apparatus which is easily fitted together is shown in Fig. 2. It consists of four large U-tubes arranged side by side in pairs. The U-tubes are mounted upon a wooden stand with two up- rights, to which the two pairs of tubes are wired. The first of each pair is filled with soda-lime, and the second with pumice soaked in concentrated sulphuric acid. Each soda-lime tube is connected with a sulphuric acid tube by well-fitting rubber corks and a bent glass tube. The two other limbs of the sulphuric acid U-tubes are joined by a three- way-tap forming a T-piece. The free end of the T-piece is attached to a small bulb tube, Fig. 3, containing a drop of concentrated sul- phuric acid to mark the rate at which the bubbles are B^.bg' through the FIG. 3. iratus. The is. connect§$, \with the combustion tube by a short M/ce of rubber tuning and a short glass tube, which passes through a rubber cork fixed in the end of the combustion tube. The rubber ".tubing carries a screw-clip. The open eno*s of FIG. 2.